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Insurance Engineering Experiment Station, 



EDWARD ATKINSON, Director. 



No. 31 MILK STREET, BOSTON, MASS. 



PROF. CHARLES L. NORTON, in charge. 



JOSEPH P. GRAY, Consulting Engineer. 



SUPERVISORS. 

The Board of Directors of the Boston Manufacturers Mutual Fire Insurance Company. 



EDWARD ATKINSON, 
FKHDERIC AMORT, 
GEORGE DEXTER, 
HOWARD STOCKTON, 

EDWARD ATKINSON, President 



JONATHAN CHACE, 
CHARLES W. AMORY, 
WILLIAM H. BENT, 



ARTHUR T. LYMAN, 
GEORGE S. SILSBEE, 
SIMEON B. CHASE, 



THEOPHILUS PARSONS, 
ARTHUR B. SILSBEE, 
EDWARD T. PIERCE. 



JOSEPH P. GRAY, C. E., Vice-President. 



REPORT No. IX. 



The Protection of Steel from Corrosion, 



BOSTON, MASSACHUSETTS, U. S. A. 
December, 1903. 



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THE PROTECTION OF STEEL FROM CORROSION. 



INTRODUCTION. 

In our first report upon the corrosion of steel, No. IV., the results given of tests to that 
date were more of a negative than of a positive character, indicating the causes of danger more 
than the methods of prevention. Subsequent experiments and investigations have developed 
methods of prevention, as yet limited, but effective in many of the most dangerous points where 
corrosion may occur ; notably in the footings of steel-framed buildings when of necessity placed 
in damp ground. It may be suggested that however remote may be the causes of hazard in the 
superstructure, steel embedded in or adjacent to damp ground in the neighborhood of the cur- 
rents of electricity of the trolley tracks, must be protected not only from the ordinar}^ dangers of 
corrosion, but from the electrolysis, which is so destructive in respect to thick cast-iron water 
pipes. Professor Norton's report will also suggest other positive elements in the case, while 
disclosing the causes of hazard yet more fully than in our previous report. 

Whether or not the steel footings or supports of high buildings, when embedded in damp 
ground, may be corroded by electrolysis from leaking currents from an electric trolley track, is 
surely a problem which requires immediate solution. If there is such a danger it may perhaps 
be met in existing buildings by encasing the footings of such buildings in an asphalt concrete, 
absolutely impervious to moisture. Dry steel may carry electric currents without injury. The 
electrolysis or dissociation of the steel occurs when the current leaves the metal, passing into damp 
ground or other wet substances. Possibly a remedy, if this evil exists, may be found by at- 
taching a conducting wire to the steel footing and thus carrying the electricity derived from the 
trolley track to some other point. Of course such currents should be cut off if possible lest they 
cause danger in steel-framed buildings above the footings or supports. 

PAINTS. 

The subject of paints will now be taken up for thorough investigation, apparatus having 
been invented and methods of testing devised, which are submitted in this report. From the 
best information that I have been able to gather on this matter, it would appear that any paint 
on which reliance can be placed for the protection of steel or other metal from corrosion must 
be one which dries by evaporation or sets like hydraulic lime : it must not be one which hardens 
by the oxidation of the oil or any other ingredient of the compound in which lead or other 
pigments are mixed. Steel, having great affinity for oxj^gen, is corroded by the oxidation of 
the oil itself, while the outer surface of the paint, exposed to the air, may stop moisture from 
penetrating for a very considerable period of time, or until the oxidation of the body of the oil 
has released the lead or other pigments, thus exposing the steel surface to a humid atmosphere 
by the complete destruction of the paint. 

Steel may be protected by paints, cements or coverings that have more affinity for oxygen 
than steel itself. Such coverings will absorb from the atmosphere, even when humid or loaded 
with particles of oxidizable matter, all that would tend to corrode before it reaches the steel. 

It is in that direction that efforts have been made, and are now being made, for making 
paints or thin veneers for the covering of steel that will neither corrode it by their own contact 
or permit corrosive elements to reach the steel. Such paints or veneers must not be brittle. 
They must be sufficiently elastic to yield to the contraction and expansion of the steel without 
cracking or chipping. We have information of one such paint, made for many years in Eng- 
land by a secret process, which has been used upon the British ships for a long period and now 
being made in this country. Under these conditions the investigations which we now propose 
to undertake seem to the undersigned to be of the gravest importance. 

Respectfully submitted, 

EDWARD ATKINSON, 

Director. 
Boston, Mass., U. S. A. 
December 26, 1903. 



THE PROTECTION OF STEEL FROM RUST. 



Since the publication of report No. IV., in which was given an accovmt of some laboratory 
experiments which showed the great degree of protection afforded structural steel by Portland 
cement concretes, the experiments have been carried on continuously. 

RESULTS. 

All the early tests which were carried out on perfectly clean steel have now been repeated 
on specimens in all degrees of initial corrosion, with the same results as shown in the case 
of the chemically clean steel. Doubt existed in the minds of some engineers as to whether the 
results as found with clean steel would apply to rusty or dirty steel. The method adopted in 
the early test was to imbed the specimens in blocks of concrete about 3'' x 3" x 8", allow them 
to set under ordinary conditions and then expose them to changing conditions of warmth, mois- 
ture, and to carbon dioxide, with traces of sulphurous gases and ammonia. Under these 
conditions unprotected steel vanished into a streak of rust, but protected by an inch or more 
of sound Portland cement concrete the clean steel was absolutely unchanged. We can now 
state further, that this same protection is afforded any ordinary structural steel of that degree 
of cleanliness likely to be found in use for building. 

SPECIMENS. 

The origin of many of the specimens was rather obscure, as the more corroded ones were 
taken from scrap heaps of steel works, many having been exposed to the weather for several 
years. Some had been in buildings as part of the structure, some in salt water, some in fresh 
water, some in damp ground, and the rest exposed to air under various conditions of dampness. 
The degree of rust on the specimens varied greatly, from a light yellowish stain to a scale 
more than one-eighth inch in thickness. 

PROCEDURE. 

The specimens were first cut to a size such that their length was not far from three inches 
and their width about one inch. They were of all thicknesses from Vso" to i%". Some were 
cut dry, some in water, some with the mill fed with oil, and a part of these cut with oil were 
cleaned with gasoline, and a part with alkaline solutions, while a third part were left more or 
less oily. It was intended that the specimens should include everything met with in regular 
practice. 

Each specimen was stamped and the blows of the steel stamp were sufficient to loosen any 
rust or scale that was not firmly attached, and a vigorous brushing with a soft wire brush 
removed any loose dust. Each piece was next weighed, and then calipered at several points, 
and incorporated in a block, or brick, of concrete, sufficiently large to cover it everywhere to a 
depth of one inch and one-half. The mixture was one part cement, two and one-half parts 
sand, and five parts broken stone in some cases, and one part cement, three parts sand, and six 
parts cinders in others. The cements used were Alpha, Lehigh, and Alsen, and care was 
taken in selecting the sand and stone. The latter was of such size as to pass a one-inch mesh. 
The concretes were allowed to set twenty-four hours in air and seven days in water, and were 



then divided into three groups, one being set out-of-doors, one stored in a damp and odorous 
basement underground, and the third being treated in the "corroders " or steam and carbon 
dioxide tanks. These galvanized iron tanks were supplied intermittently with steam, hot water, 
moist air, dry air, and quite continuously with carbon dioxide for periods of from one to three 
months. There were a number of specimens which were further exposed in tide water, in 
sewers, over furnaces, with constant contact of furnace gases. 

CONDITION OF SPECIMENS. 

After varying lapses of time from one to three months for the specimens in the " corroders," 
and from one to nine for the others, the specimens were broken out of the briquettes, cleaned 
by brushing, and weighed and calipered. Not one specimen had shown any sensible change 
in weight or dimension, except where the concrete had been poorly applied. Some specimens 
were purposely bedded in very dry concrete, and some in concrete partly set, and many of these 
were not well covered and the steel was seriously attacked where there were voids or cracks. 
Of the hundreds of specimens of rusty steel examined not one which had a continuous, 
unbroken coating of concrete, gained or lost anything in volume or weight by treatment which 
caused the practical destruction of some of the unprotected specimens. If loss by corrosion as 
great as ^4ooo of the loss occurring with the unprotected specimens had been experienced in the 
case of the protected pieces it would have readily been noted. 

CONCLUSIONS. 

It would therefore seem that if we admit that from a severe trial of a short duration, we 
may judge relatively of the effects of the less severe but longer test of time, it can not be 
questioned that structural steel is safe from corrosion if incased in a sound sheet of good 
concrete, at least for a period of years so long as to make the subject of more interest to our 
great-grandchildren's children than to us. We know that bare steel does not rust and fall down 
over night, and that much of the steel standing has been bare of everything that could protect 
it, for long years, and it seems to me beyond question that steel properly covered in concrete 
may well be expected to last far longer than the changes in our cities will allow any building 
to remain. 

There is one limitation to the whole question, that is the possibility of getting the steel 
properly incased in concrete. Many engineers will have nothing to do with concrete because 
of the difficulty in getting "sound" work. This is especially true of cinder concrete, where the 
porous nature of the cinders has led to much dry concrete and many voids, and much corrosion. 
I feel that nothing in this whole subject has been more misunderstood than the action of cinder- 
concrete. We usually hear that it contains much sulphur and this causes corrosion. Sulphur 
might, if present, were it not for the presence of the strongly alkaline cement ; but with that present 
the corrosion of steel by the sulphur of cinders in a sound Portland concrete is the veriest myth, 
and as a matter of fact the ordinary cinders, classed as steam cinders, contain only a very small 
amount of sulphur. There can be no question that cinder-concrete has rusted great quantities 
of steel, but not because of its sulphur, but because it was mixed too dry, through the action 
of the cinders in absorbing moisture, and that it contained, therefore, voids ; and secondly, 
because in addition the cinders often contain oxide of iron which, when not coated over with 
the cement by thorough wet mixing, causes the rusting of any steel which it touches. 

There is one cure and only one, mix wet and mix well. With this precaution I would 
trust cinder-concrete quite as quickly as stone concrete in the matter of corrosion. It has been 



suggested that steel which has been rusted to a slight depth becomes protected by this coating 
from further rusting. Nothing could be further from the truth. A large number of specimens 
were rusted by repeated alternate wetting and drying to see if they finally reached a constant 
condition. Instead of doing this, they all showed an irregular but persistent loss in weight, on 
further rusting, until some had practically been washed away. 

The increasing use of steel of small dimension in floors and roofs, twisted rods, expanded 
metal, etc., has caused some question as to the advisability of their use in view of the possible 
great effects of corrosion, as compared with the effects of corrosion on larger members, but 
with sound concrete of a thickness of about one and a half inches between the steel and the 
weather I do not question the durability of these lighter members. 

The destruction caused to steelwork by rust is certainly not more appalling in most 
instances, at least , than that caused by electrolysis. The action here is more apt to be local, and 
hence more dangerous in that inspection or protection of other parts of a structure will not 
indicate or prevent impending disaster to the one member which may serve as the point of 
departure of the escaping electric current. No satisfactory treatment other than some sort of 
waterproofing has appeared to be successful, and study of this matter is going on at present in 
many places. It is a problem for the chemist rather than for the engineer. 

The next step in this research is to find out in the same general way the degree of protection 
afforded by paint, and second, by brick and tile work. This is now under way and the rapidity 
with which the " corroders " destroy some paints is such that a report on this subject may be 
looked for in the near future. 

The investigation of the relative efficiency of different paints as a protective coating for 
structural steel being now under way, it is desired that all kinds of paint be submitted to our test 
of exposure to varying conditions. To this end we invite all dealers and manufacturers of paint, 
for this purpose, to send samples to the amount of one gallon to Professor C. L. Norton, 
Room A, Walker Building, Massachusetts Institute of Technology, with any directions for 
applying the paints to either clean or ordinarily rusty steel. The results of these tests will not 
be published without the consent of the persons submitting the paint to test. 

Some pieces of steel will, after coating with the paint under test, be submitted to various 
corrosive influences, and the details of the exposure being such as will correspond in nature to 
the actual exposure of structural steel, but of an intensified degree, it is believed that relative 
results may be arrived at in a reasonably short time in this way. 

Respectfully submitted, 

CHARLES L. NORTON. 



LIBRftRY OF CONGRESS 



019 408 555 2 



